The present invention relates to a process for removing ammonium nitrate NH.sub.4 NO.sub.3 from aqueous solutions.
Ammonium nitrate, NH.sub.4 NO.sub.3 (hereinafter referred to as AN) is obtained as a byproduct, for example, in reprocessing processes for irradiated nuclear fuels and/or breeder elements such as, for example, in the Purex process, and is undesirable during further industrial processing of the process solutions in which it is contained. In the production of UO.sub.2 according to the ammonium uranyl carbonate precipitation process (AUC), or in the joint precipitation process of uranium and plutonium according to the ammonium uranyl plutonyl carbonate process (AUPuC), AN is obtained as a waste product. In both cases, the AN must be removed. No solution yet exists to the problem of eliminating the undesired products in the Purex process. Several processes have been proposed for the removal of AN in the AUC and AUPuC processes, but none of them constitutes a satisfactory solution.
In one prior art process, as set forth in German Offenlegungsschrift No. 2617968 in the name of P. Morschl and E. Zimmer, a basic metal oxide or metal hydroxide is added to the solution containing the AN and the solution is heated to about 100.degree. C. so as to obtain ammonia. The resulting ammonia is separated from the likewise formed metal nitrate by evaporation. Thereafter, the thus formed nitrate solution is dried and the metal nitrate is thermally decomposed to metal oxide and nitric oxides whereupon the nitric oxides are further processed to nitric acid.
In a proposal by F. Herrmann and Th. Sondermann, as set forth in German Auslegeschrift No. 2,838,007, NH.sub.4 + ions are separated electrophoretically from the NO.sub.3 - ions, and NH.sub.3 is extracted by increasing the temperature. The NO.sub.3 - ions are extracted for recycling in the form of HNO.sub.3.
According to a further process of Th. Sondermann, as set forth in German Offenlegungsschrift No. 2,901,067, for processing AN containing radioactive filtrates, as they are obtained, for example, in the AUC process or in the AUPuC process, the solution is brought to the boiling temperature with the aid of the current heat of an electrolysis current and is denitrated electrolytically. This results in free NH.sub.3 and CO.sub.2. Additionally, it has been proposed to thermally spray decompose AN containing solutions and to decompose AN with concentrated nitric acid in the presence of chlorides.
All these processes have in common that they have not yet been used industrially or under nuclear plant conditions. The thermal decomposition processes have the grave drawback that they require temperatures above 100.degree. C., that the necessary equipment is complicated with respect to material and space requirements, and that nitrous gases NO.sub.x develop.
The decomposition process with concentrated nitric acid and chlorides brings about serious corrosion problems due to the presence of the chlorides. The electrolytic processes also require complicated equipment, involve a large consumption of electrical energy and encounter anode corrosion problems.